Is it permissible to continue supplicating against those who wronged me and prevented my promotion despite my deserving it, especially after my return from Hajj and Umrah?

There is no harm in supplicating against an oppressor, even during prayer. The proof for this is the supplication of Sa'd ibn Abi Waqqas against the man who accused him. Nevertheless, patience and forgiveness are better than persistently supplicating against an oppressor, as Allah says: "And that you pardon is nearer to piety."